47 CFR 95.607 - CB transmitter modification.
Only the holder of the grant of authorization of the particular certificated CB transmitter may make the modifications permitted under the provisions for certification (see part 2 of this chapter.) No grantee shall make any of the following modifications to the transmitter without prior written permission from the FCC (Federal Communications Commission):
(a) The addition of any accessory or device not specified in the application for certification and authorized by the FCC in granting the certification;
(b) The addition of any switch, control or external connection;
(c) Any modification to provide for additional transmitting frequencies, increased modulation level, a different form of modulation, or increased TP (RF transmitter power expressed in W (watts), either mean power (TP averaged over at least 30 cycles of the lowest modulating frequency, typically 0.1 seconds at maximum power) or peak envelope power (TP averaged during 1 RF cycle at the highest crest of the modulation envelope), as measured at the transmitter output antenna terminals.)